1. Technical Field of the Invention
This invention pertains generally to the recovery of ferrous or non-ferrous materials from scrap metals bearing slags, sands, and other contaminants. More specifically, the invention pertains to a scrap separation device for recovering ferrous or non-ferrous scrap metals from mixed scrap containing slag, sands, and other contaminants and a system comprising the scrap separation device which recovers and grades the ferrous and non-ferrous scrap from a dirty scrap metal feed.
2. Description of the Related Art
Metals, in particular the metals used in steel making, play an important role in modern society and have historically been linked with industrial development and improved living standards. Metals used in steelmaking can be draw from metal resources in the Earth's crust as well as from metals discarded after use in the economy. Unlike polymer plastics, the properties of metals can be restored fully through recycling processes, regardless of their chemical or physical form or how many times the metal is recycled. However, success of the secondary metals market depends on the cost of retrieving and processing the metals embedded in used materials. The higher the concentration of metal in a used material, the easier it is to recycle.
Over 11 million tons of iron and steel scrap are produced each year. Of this amount, only about 70 percent is recovered. About ⅔ of the unrecovered iron and steel scrap is land filled. Each ton of recycled steel can save 1.5 tons of iron ore, 0.5 tons of coal, 40% of the water used in production, and 75% of the energy needed to make the steel from the raw materials, and represents a 1.28 ton reduction of solid waste into the waste stream, an 86% reduction in air emissions, and a 76% reduction in water pollution (from the Bureau of International Recycling; http://www.bir.org).
The production of steel also introduces a large amount of material into the waste stream. In addition to the excess material generated during sand casting of steel parts, more than 400 million tons of iron and steel slag is produced each year (from the World Steel Association; www.worldsteel.org). Slag is a mixture of silica, calcium oxide, magnesium oxide, and aluminum and iron oxides. During steel making, slagging agents and fluxes (mainly limestone or dolomite and silica sand) are added to the blast furnace to remove impurities from the iron ore, steel scrap, and other ferrous feeds. The slag protects the liquid metal from outside oxygen and maintains temperature by forming a lid. As such, there is always a certain amount of steel and/or iron trapped in the slag. Beyond the losses of potentially valuable steel and iron in this slag waste, landfilling of these waste products has become increasingly costly.
For years, steel producers have only attempted to recover the larger pieces of steel and/or iron trapped in the waste slag. While this results in a waste slag product that retains a significant portion of unrecovered steel and/or iron, as mentioned above, the concentrations have not been high enough to make the material cost effective for extraction and use in the steel producing process. However, with the recent increases in the prices of raw steel and iron and the energy necessary to produce steel, and the increased cost of landfilling the slag waste, recovery of the iron and/or steel contained in the waste slag has become more important. In addition, once the steel and/or iron are removed from the waste slag, the resulting size graded aggregate can be used in various products, such as in construction aggregate, in concrete products, in road bases and surfaces, and as fill, clinker raw material, railroad ballast, roofing, mineral wool (for use as insulation) and soil conditioner.
Systems known in the art for recovering steel and/or iron from the waste stream, particularly from slag and green mold castings, typically use magnetic separators and impacting devices. The impacting devices are generally rotary tumblers equipped with blades or teeth that lift and drop the waste material in an effort to dislodge the slag or sands. Certain devices have further included a solid media which may provide further scrubbing action. More recent rotary devices have also included a crushing means to reduce the size of the input material. However, none of the prior art devices provide a means other than impact or abrasion to free the steel and/or iron from the contaminating slag or sands. Furthermore, none of the prior art systems provide a means for recovery of size graded contaminating slag and sands, or size grading of the recovered scrap metal.
Accordingly, there exists a need in the prior art for a device and system which may be used to recover ferrous materials such as steel and iron from scrap metals which are contaminated with slag, sands, and other contaminants. Additionally, there exists a need in the prior art for a device and system which may partition the purified steel and iron into various size grades, and may also partition the recovered contaminating slag and sands into various size grades.